Most Ionisers are not recognised by Australian standards so be warned. It is not recommended to use any system that simply dissolves solid copper into the water. Whilst copper is a good bactericide it is actually toxic in too large a dose to humans. The best Ionisers are called Nature2, these use Copper / Silver nitrates held within a canister and they are NOT released into the pool. These units are a better option for an above ground because you don't have the corrosive properties associated with salt water.
If you are going to stay with hand dosing your above ground pool then it is generally accepted that dry chlorine is less corrosive than liquid chlorine so your pool will last longer. A correctly maintained above ground pool should last 10 to 15 years.